Added lookup table system to TimingData so that GetBeatAndBPS and GetElapsedTime don't have to walk through the entire list of timing segments several times every frame during gameplay.

src/ScreenGameplay.cpp

@@ -1486,6 +1486,13 @@ void ScreenGameplay::StartPlayingSong( float fMinTimeToNotes, float fMinTimeToMu
 	UpdateSongPosition(0);
 
 	ASSERT( GAMESTATE->m_Position.m_fMusicSeconds > -4000 ); /* make sure the "fake timer" code doesn't trigger */
+	FOREACH_EnabledPlayer(pn)
+	{
+		if(GAMESTATE->m_pCurSteps[pn])
+		{
+			GAMESTATE->m_pCurSteps[pn]->GetTimingData()->PrepareLookup();
+		}
+	}
 }
 
 
@@ -2548,6 +2555,13 @@ void ScreenGameplay::SaveStats()
 
 void ScreenGameplay::SongFinished()
 {
+	FOREACH_EnabledPlayer(pn)
+	{
+		if(GAMESTATE->m_pCurSteps[pn])
+		{
+			GAMESTATE->m_pCurSteps[pn]->GetTimingData()->ReleaseLookup();
+		}
+	}
 	AdjustSync::HandleSongEnd();
 	SaveStats(); // Let subclasses save the stats.
 	/* Extremely important: if we don't remove attacks before moving on to the next